Re: [PATCH v2 08/11] x86/boot: place trampoline code in a non-execute section

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 01/04/2025 2:08 pm, Roger Pau Monne wrote:
> The trampoline code is never executed in the position placed by the
> loader.  It's first copied to the low 1MB, and always executed from
> there.
>
> Move the trampoline code from being in .init.text section into
> .init.data, so it's not in an executable section.  This allows applying
> the relocations safely against a non-executable (and thus non-read only)
> section, and then copy the relocated trampoline to the low 1MB.  Note
> that the trampoline code is placed on an .init section, so zapped after
> boot has finished.
>
> No functional change intended.
>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> An alternative approach is to apply the relocations after having copied the
> trampoline to the low 1MB, but that still generates relocations in mkreloc,
> which is not helpful for the goal of having no relocations applied to
> read-execute code sections.  This approach however places code in a data
> section, which might cause issues when debugging it.

I, probably most of all, spend a reasonable amount of time disassembling
the trampoline. I really would prefer to keep it in an executable section.

What are the options with relocations?  Can't we simply drop any in the
trampoline region?

~Andrew